Mr Li and Mr Wei are Chinese nationals. The investigation was carried out by the US Fish and Wildlife Service.

According to prosecutors, Mr Li sent hundreds of thousands of dollars to a co-conspirator in the US to buy rhino horns, which were sent in porcelain vases to another person in Hong Kong, in an effort to evade US authorities.

'Good health'

Mr Li is also accused of trying to buy two rhino horns for $59,000 (£38,000) in a hotel room in Miami in January from an undercover fish and wildlife officer. He also asked the undercover officer to procure more horns and send them to Hong Kong.

Mr Wei, who was sharing a hotel room with Mr Li, later asked an undercover informant to take a fish and wildlife officer out for dinner and offer her money to help Mr Li, prosecutors said.

Meanwhile, prosecutors say Mr Wang bought libation cups carved from rhino horn in the US and sent them to Mr Li in Hong Kong.

Some believe drinking from intricately carved rhino horn cups brings good health, and the cups are highly prized by collectors, US authorities said.

Native to Africa, the black rhinoceros is classified as a critically endangered species, according to the Convention on International Trade in Endangered Species of Wild Fauna and Flora.

But demand for rhino horns and the prices paid for them on the black market have soared in recent years, US prosecutors said.